The present invention relates generally to nuclear reactors and more particularly to apparatus for servicing the core of nuclear reactors.
In nuclear reactors, it is generally necessary to provide neutron absorber control elements and additionally, various types of instrumentation for servicing the nuclear core, particularly during operation of the reactor. Such servicing elements typically enter the reactor through penetrations in a head portion of the reactor. In some instances, separate penetrations are provided for neutron absorbers and others for the instrumentation, and in other instances a neutron absorber and instrumentation may be combined in a single package, there being a multiplicity of such arrangements for the reactor.
Further, in certain types of reactors, particularly liquid metal cooled fast breeder reactors, it may be desirable to refuel a reactor without removing the head. This aids in preventing the contact of liquid metal coolant such as sodium, with air and further avoids the release of fission gases. To accomplish the refueling, rotating plugs or shields which serve to close off and seal the reactor vessel during normal reactor operation have been used previously. One example of such an arrangement is seen in U.S. Pat. No. 3,354,040 to A. G. Frame et al. While that patent shows a single large rotating head with a mechanism which transfers fuel between the core and a magazine housing within the environment of the core, other such reactors have incorporated one or more smaller rotating plugs within the large plug and provide fuel transferring apparatus for removing the fuel directly from within the reactor vessel.
In any event, it becomes desirable to reduce the number of penetrations to the head and/or to reduce the size of the penetrations. Such reduction in number of penetrations and size of penetrations serve both to enhance the strength of the head and to allow greater flexibility and replacement of any smaller rotating plugs which may serve to support fuel handling apparatus during refueling.
The above-mentioned Frame patent combines several instrument packages with the neutron absorber for each core servicing assembly which penetrates the rotating head. However, the lateral dimension of the head penetration required to receive each such servicing assembly is relatively large creating some of the drawbacks mentioned above.
More recently, in U.S. application Ser. No. 537,283 for "Control Rod and/or Instrument Tree Assembly" by Noyes et al, filed Dec. 30, 1974, there is disclosed core servicing apparatus which comprises a plurality of assemblies each removably mounted to penetrations in the reactor head and including means for laterally displacing a plurality of servicing elements from a compact to an expanded configuration. The core servicing apparatus of that application has the advantage of being initially installed in the region of the core through a relatively small diameter penetration in the reactor head and allowing lateral displacement of a plurality of core servicing elements such as instrument probes. In the preferred embodiment, this lateral displacement of the core servicing elements is accomplished by the outward deflection of downwardly inserted instrument probes and their accompanying flexible cables.
In another somewhat related application, U.S. application Ser. No. 537,284 for "Core Servicing Apparatus" by Dupen, filed Dec. 30, 1974, lateral displacement of the servicing elements from a compact to an expanded configuration is accomplished through the use of a plurality of pantograph support arms. The pantograph support arms serve to provide more accurate placement of the servicing means with respect to the assemblies of the core.
It is to an alternative core servicing apparatus, especially one which is compatible with both line of sight through the head refueling and relatively small assembly size, that the present invention is directed.